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Abstract
In this paper, we analyze the frequency-dependent feature of the human body as radio propagation channel and the influence of that characteristic on the design of antennas for body-based applications. We describe the main impairments due to the frequency dispersion propagation through the body channel. Firstly, we describe the formation of the electromagnetic fields called Brillouin precursors which are responsible for another vital impairment: broadening of the time width of a transmitted signal. Later, we show a theoretical radio channel characterization of a human tissue that is affected by the frequency dispersion. Following, we describe three solutions to the described problematic optimal design of waveforms matched to the body channel, anti-dispersive filtering, and optimal antenna design. We introduce two broadband antennas offering a flat frequency response, minimizing the formation of precursors that ensures optimal time domain performance for ultrawideband body-based applications. Finally, we discuss the relation between the precursor formation and the parameters adopted to quantify the electromagnetic absorption inside biological tissues in order to review its definition under the dispersive perspective.